Oscillatory high-voltage supply



Feb. 1, 1955 G. D. HULST 2,701,310

OSCILLATORY HIGH-VOLTAGE SUPPLY Filed Jan. 12, 1949 IIII 9a(II|I. 7 9HIIII I IIII Illu I ||||II||| 3 I... I IIIIII I 9c6' l1m I IIIIIIIII-(LIIIII I'll l l IIIIIHIIUW Fig. 3

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GEORGE D. HULST Fig. 2

A T TORNEYS United States Patent OSCILLATORY HIGH-VOLTAGE SUPPLY GeorgeD. Hulst, Upper Montclair, N. J., assignor to Allen B. Du MontLaboratories, Inc., Passaic, N. J., a corporation of DelawareApplication January 12, 1949, Serial No. 70,546

4 Claims. (Cl. 250-36) This invention relates to high voltage low powerdirect current supply circuits of the radio frequency oscillator typeand more particularly to a high voltage supply particularly adapted foruse in television apparatus.

In the prior art (U. S. Patent No. 2,276,832) an oscillator circuit hasbeen utilized to provide direct current for a cathode ray tube such asis used in television apparatus. In these circuits, it has beencustomary to use a transformer having primary, secondary, and tertiarywindings, these windings being connected to the plate of the oscillatortube, the high voltage rectifier, and the grid of the oscillator tube,respectively.

It has been found that, to obtain good regulation from such a supply,the primary and secondary circuits must be reasonably tightly coupled(U. S. Patent No. 2,374,781). It has also been found in practice thatthe spacing between the high voltage winding and other wind ings mustnot be less than a certain amount dependent upon voltage, in order toavoid corona and high voltage fiashover, which if present would generatenoise in the amplifiers associated with the cathode ray tube and mightresult in damage to the coil itself.

It is an object of this invention to provide a high voltage supplyhaving good regulation, high efliciency, and low short circuit current.

A second object is to provide a high voltage supply which is free ofcorona, compact, and inexpensive to manufacture.

These objects are accomplished in part by the incorporation of a highvoltage transformer which has certain novel constructional features.

The objects and features of my invention can best be understood byreferring to the accompanying drawings, in which:

Figure 1 is a side elevational view showing a high voltage transformerincorporating the novel features of this invention;

Figure 2 is a schematic drawing of a circuit in accordance with oneembodiment of my invention incorporating the transformer of Figure l;and

Figure 3 is a graph illustrating the performance obtainable from myinvention.

Referring to Figure 1, the high voltage transformer comprises a coilform upon which are wound a primary winding 2, a high voltage secondarywinding 3, and a tertiary winding construction in accordance with theinvention, to be explained in more detail hereinafter.

The start or inside end of the primary winding 2 is soldered to aconnecting lug 4. The finish or outside end of the primary winding 2 issoldered to a second connecting lug 5. The start or high voltage end ofthe high voltage winding 3 is connected to a high voltage wire 6 whichhas a large diameter insulating covering to insure against corona. Aconnector 7 having a smooth rounded outside contour is used to terminatethe high voltage wire 6 and to connect it to the high voltage rectifiertube (shown in Figure 2). In the preferred form shown, one turn of thehigh voltage wire 6 is afiixed to the top end of the coil form 1 to forma corona shield 8 for the coil form. The secondary winding 3 is woundcontinuously in the form of five separate pies or coils 9a, b, c and d,and 10. in a manner known to the art, in order first to keep thepotential difference between adjacent turns of wire to a safe value andsecond to keep the distributed self- "'ice capacitance of the highvoltage winding to a low value. The last pie 10 of the secondary winding3 is provided with a tap 11, the purpose of which will be explained. Thefinish of the secondary winding is soldered to a connecting lug 12.

The tertiary winding is composed of two parts, one part being theportion of the secondary winding between the tap 11 and the finish, themanner of connection being that of an autotransformer. This portion ofthe secondary winding, in the embodiment shown, thus serves twopurposes. The two wires resulting from the tap 11 of the secondarywinding 3 may be soldered as a matter of convenience, to a dummy lug 13.To this dummy lug 13 also is soldered the start of the second part 14 ofthe tertiary winding, the finish being soldered to a fourth connectinglug 15.

The purpose of the special form of the tertiary winding is as follows.Since it is desirable to keep all the low voltage windings away from thehigh voltage end of the secondary winding, and since there must be morethan a certain critical amount of mutual inductance between thesecondary winding and both the primary and the tertiary windings, bothprimary and tertiary windings are located near the low potential end ofthe secondary winding. Hence it follows that there will be high mutualinductance between primary and tertiary windings. This in turn ifpresent, would result in poor operation of the high voltage supply.

The manner of minimizing mutual inductance between primary and tertiarywindings in my invention may be described in this way. One winding,preferably the tertiary winding, is wound in two parts, one part beingin close proximity to the secondary winding and one part being moredistant therefrom. The two parts of the tertiary winding are then soconnected that the mutual inductance between the primary winding and onepart of the tertiary winding is opposite and preferably approximatelyequal to the mutual inductance between the primary winding and the otherpart of the tertiary winding. If this condition holds, the mutualinductance between secondary and each part of the tertiary will ingeneral also be opposing, but since one part of the tertiary winding iscloser to the secondary winding than the other, the mutual inductanceswill be unbalanced, and adequate coupling will obtain between secondaryand tertiary windmgs.

In the preferred form shown, the nearer portion of the tertiary windingis a part of the secondary winding in autotransformer connection to thetap, rather than being a separate coil. The reasons for this are thoseof economy, rather than of principles. In the first place, one lesswinding position of the coil is required in manufacture. In the secondplace, if a separate coil were used it would have to be spaced as faraway from the low potential pie 10 as the coil 14 in order to have asufficiently low potential gradient along the surface of the coil form.In the third place an autotransformer connection requires less wire thana separate coil if the latter has the same mutual inductance.

In Figure 2 is shown a preferred circuit in which the coil of Figure 1may be used. An oscillator tube 17 preferably of the beam power type hasits plate connected to a primary winding 2 of a high voltage transformer18, of the type shown in Figure 1. The other end of the primary winding2 is connected to a source 19 of direct current. In parallel with theprimary winding 2 of the transformer and of such a value to resonatetherewith are a fixed capacitor 20 and an adjustable capacitor 21. Thescreen grid of the oscillator tube 17 is connected through a resistor 22to the source. 19, the screen grid being bypassed to the cathode of theoscillator tube 17 by means of a condenser 23. The grid of theoscillator tube is connected to the parallel combination 24 of aresistor and a capacitor, for the purpose of providing grid bias, thecombination 24 in turn being connected to the lower portion 14 of thetertiary winding by means of a terminal 15. The cathode of theoscillator tube 17 is connected to the low potential end ofthe'secondary winding 3 by means of a terminal 12. The upper and lowerportions of the tertiary winding are connected together by means of adummy lug 13. The secondary winding 3 of the transformer is connected toa load 25 which in the preferred form contains a high voltage rectifier26, a resistance-capacitance filter 27, and a cathode ray tube 28, saidcombination being well known to the art.

The amount of voltage obtainable from the supply can be controlled bymeans of the oscillator plate tuning condensers 20 and 21. An increaseof capacitance results in a lower no-load voltage.

In Figure 3 is shown a curve representative of the performanceobtainable from the preferred circuit of Figure 2. When the picture onthe face of the cathode ray tube is completely black, i. e. when theselection beam is not exciting the screen, the high voltage supply drawsno current and its operation is represented by the intersection 29 ofthe performance curve 30 and the zero current line. As the subjectmatter portrayed on the picture tube becomes brighter, current is drawnfrom the supply and the voltage drops slightly as represented by theflat portion 31 of the performance curve 30. With an extremely brightpicture full rated current flows. In the preferred form of the supply,the full load current coincides with a flexure point 32 on theperformance curve. It is desirable that the voltage between no-load andfull load operation remain fairly constant, this condition being knownas good regulation. Stated another way, the slope of the flat portion 31of the performance curve is the internal resistance of the supply overits operating range, which slope should be low. In the preferred circuita supply adjusted to give 17.5 kilovolts at no load has approximately3.5 megohms internal resistance between no load and a full load of 700microamperes.

Beyond the operating range it is desirable that the performance curvedrop quickly to zero, so that the maximum current that can be drawn fromthe supply is low. If this condition exists accidental contact ofpersonnel with the supply will not represent a hazard. In view of thedual need for good regulation and low maximum current it becomesapparent that the flexure point must preferably be sharp and Welldefined at approximately the desired full load or a little above it. Ithas beenfound in practice that this condition exists only when themutual inductance between the primary and tertiary windings is verysmall. This invention makes possible the desired regulation whileconfining the maximum current represented by point 33 well below thelimit set by insurance underwriters.

It has been found that the improved performance of the described supplyresults in part from the low self capacitance of the high voltagewinding which in turn results from the complete removal of all lowvoltage windings from the proximity of the high voltage end of the highvoltage winding, as has been described.

The efiiciency of the supply usually increases with the size of thetransformer, higher Q in the windings being obtainable. Since the lowvoltage windings are grouped together, in a given amount of space, thesecondary winding may be made larger than in the transformer usedheretofore, resulting in unusually high efficiency.

In the preferred circuit the components have the following values:

Tube 17-6L6G Transformer 18:

Primary winding, .00034 henry Secondary winding, .24 henry Tertiarywinding, .00034 henry Mutual inductance, primary to secondary, .0019

henry Mutual inductance, secondary to tertiary, .00l2

henry Mutual inductance, primary to tertiary, none Supply 19, 425 voltsCapacitor 20, .0028 microfarad Capacitor 21, .005 to .0015 microfaradResistor 22, 33,000 ohms Capacitor 23, .05 microfarad Combination 24,47,000 ohms and .00047 microfarad Rectifier 26, 1B3 Filter 27, 100,000ohms and .0005 microfarad Cathode ray tube 28, 20AP4 Although the abovecomponents gave excellent results for the particular application forwhich they were used, the values selected are not critical. The value offixed capacitor 20 should be selected for the particular output voltagedesired. For many applications, the adjustable condenser 21 may beomitted. In all cases, however, the mutual inductance between primaryand tertiary winding should be small.

In the claims, a low voltage winding signifies that transformer windingconnected to the input voltage supply source while high voltage windingsignifies that winding connected to an output or utilizing loadrequiring a voltage greater than the input voltage. Specificallyapplying the terms When utilizing an electronic oscillator, the lowvoltage windings are connected to the oscillator voltage supply whilethe high voltage winding is connected to the utilizing electronic tubesuch as a cathode ray tube.

It should be understood that although a specific embodiment of myinvention has been shown and described, other embodiments suitable forother desired conditions can readily be devised by those skilled in theart. The extent of these embodiments can best be ascertained from thefollowing claims.

What is claimed is:

l. A device for supplying electrical power to a load, said devicecomprising an oscillator tube having input and output circuits, and atransformer comprising a first winding connected in one of saidcircuits, a second winding mutually inductively coupled to said firstwinding and electrically connected to said load, and a third windingadjacent said first winding and connected electrically to the other ofsaid circuits, said third winding having separate parts, each of saidparts being positioned to couple inductively in unequal magnitude tosaid second winding and in equal magnitude to said first winding, andbeing electrically connected together in coupling opposition withrespect to said first winding.

2. A device for supplying electrical power to a load, said devicecomprising an oscillator tube having input and output circuits, and atransformer comprising a first winding connected in one of saidcircuits, a second winding positioned near said first winding andconnected to said load and having high and low potential ends and a tapintermediate said ends, and a coil positioned adjacent and inductivelycoupled to said first winding, and connected in the other of saidcircuits in series with the portion of said second winding between saidlow potential end and said tap in coupling opposition with respect tosaid first winding, said coil and said portion of said second windingbeing inductively coupled to said first winding in equal magnitude.

3. A device for supplying electrical power to a load, said devicecomprising an oscillator tube having a grid, a plate, and a cathode, anda transformer comprising a first winding connected in series with adirect voltage source between said plate and said cathode, a secondwinding connected to said load and having high and low potential endsand a tap intermediate said ends and a coil positioned adjacent to andinductively coupled to said first winding, and connected in series withthe portion of said second winding between said low potential end andsaid tap between said grid and said cathode in coupling opposition tosaid first winding, said coil and said portion of said second windingbeing inductively coupled to said first winding in equal magnitude.

4. A transformer comprising a first winding, a second winding positionedto be inductively mutually coupled to said first winding and having highand low potential ends and a tap intermediate said ends, and a thirdwinding positioned adjacent and inductively coupled to said firstwinding and connected electrically to said tap in coupling opposition tothe portion of said second winding between said tap and one of saidends, said third winding being inductively coupled solely to said secondwinding.

References Cited in the file of this patent UNITED STATES PATENTS1,628,806 Reijnders May 17, 1927 1,706,837 Bailey Mar. 26, 19291,723,485 Kummerer Aug. 6, 1929 1,775,880 Whitlock Sept. 16, 19301,873,665 Rigante Aug. 23, 1932 1,992,100 Stein Feb. 19, 1935 (Otherreferences on following page) 5 UNITED STATES PATENTS Sams et a1. July9, 1935 Lucke et a1. Feb. 21, 1939 Moller et a1. Oct. 22, 1940Broekhuysen Apr. 1, 1941 Bahring Dec. 9, 1941 Zuschlag Dec. 30, 1941Weagant Feb. 23, 1943 Zuschlag Sept. 21, 1943 Camilli June 27, 1944 6Wheeler Mar. 23, 1948 Clapp Mar. 23, 1948 Foster June 8, 1948 GermannApr. 12, 1949 Singh Dec. 13, 1949 Gannaway Mar. 27, 1951 FOREIGN PATENTSFrance Aug. 13, 1930 France Dec. 31, 1937

